Re: Towards a classification system for uses of the Private Use Area

From: Mark Davis (
Date: Fri Apr 26 2002 - 12:51:34 EDT

I agree that elaborate PUA schemes will not see any public acceptance.
The most practical use we've seen is as a holding area for characters
transcoded from Asian character sets that are not in the Unicode
Standard (they *may* end up in it in the future, or not; or may be
represented as variant sequences (see U3.2).)

That mechanism does allow for round-tripping (at least internally, and
*if* the text is not mixed with PUA characters from other sets). Not
an ideal solution, but one that meets certain needs. See


Γνῶθι σαυτόν — Θαλῆς
[For transliteration, see]

----- Original Message -----
From: "Doug Ewell" <>
To: <>
Cc: "Michael Everson" <>; "William Overington"
Sent: Friday, April 26, 2002 08:50
Subject: Re: Towards a classification system for uses of the Private
Use Area

> Michael Everson <> wrote:
> > The Private Use Area is not to be classified. Anyone anywhere can
> > any of its code points for anything.
> Furthermore, even if William's scheme is intended to be a
> "convention" rather than an official part of Unicode -- much like
> Michael's (and John Cowan's) own ConScript Unicode Registry -- it
> unlikely that an elaborate indexing scheme such as the one William
> proposes would gain much of a following. Vendors have only recently
> started to implement surrogates properly, and still balk at decoding
> SCSU (which is easy; it's the encoding part that gets complex). And
> these official Unicode mechanisms are simple compared to William's
> point" indexing scheme.
> Additionally, it is VERY important to repeat -- probably more
> than anything else in this discussion -- that there is no automatic
> to "promotion" of any private-use character to full Unicode status.
> Every character and script that is encoded in Unicode must undergo
> same scrutiny, regardless of how (or whether) it may have been
> in the past. That goes for Deseret and Shavian (accepted) as well
> Klingon and Aiha (not accepted), all of which were encoded in
> but none of which were automatically "promoted" on that basis alone.
> There are two full Private Use planes, 131,068 code points in all
> counting the four noncharacters), certainly enough for any
> implementation that would be envisioned as benefiting from William's
> proposal, and a lot easier to implement (and thus more likely to be
> used). My suggestion to William is that if he envisions a
> widespread use for the PUA, he may consider creating a
> registry for the upper planes. That would be just as effective and
> simpler.
> Apart from font vendors who use the PUA for presentation forms
> the font, what current practices exist for using the PUA? I
> ConScript; how popular is its use? Are there any other commonly
> practices or conventions? Apple has blocked out a code point for
> SIGN, and somebody (sorry, don't remember the name) mentioned a
> Microsoft convention of a subarea for symbols or dingbats. Maybe a
> discussion along these lines can reveal the true nature of PUA use
> help William redirect his considerable energy toward a more
> system.
> -Doug Ewell
> Fullerton, California

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